Today’s Tidbits: December 10, 2018

Here are SpacePolicyOnline.com’s tidbits for December 10, 2018: water on Bennu, wind on Mars, Voyager 2 goes interstellar.  Be sure to check our website for feature stories and follow us on Twitter (@SpcPlcyOnline) for more news and live tweeting of events.

Water on Bennu

NASA’s OSIRIS-REx asteroid sample return mission just arrived at its destination, the asteroid Bennu, last week and has already sent back new scientific findings.  Bennu has water.

Liquid water is essential to life as we know it, so scientists are always excited when water in any form is found on other solar system bodies.  In this case, it is not liquid, however.  Instead, the water is bound up in clays.  NASA says that “[w]hile Bennu itself is too small to have ever hosted liquid water, the finding does indicate that liquid water was present at some time on Bennu’s parent body, a much larger asteroid.”

OSIRIS-REx is currently surveying the asteroid, flying over it in passes that take it as close as 4.4 miles (7 km) to better determine its mass.  The mass affects the asteroid’s gravitational pull on the spacecraft so its value is needed before the spacecraft enters orbit. That is scheduled for December 31.  Eventually, OSIRIS-REx will use an instrument called TAGSAM to make a touch-and-go (TAG) to collect a SAMple and return it to Earth.

Amy Simon, one of the scientists working on the mission, said the sample will be a “treasure trove of new information about the history and evolution of our solar system.”  [https://www.nasa.gov/press-release/nasa-s-newly-arrived-osiris-rex-spacecraft-already-discovers-water-on-asteroid]

Listen to the Winds on Mars

Another NASA spacecraft, InSight, that just reached its destination, Mars, also is already sending back new data.  In this case, it is the first sounds of the winds on Mars.

InSight landed on November 26.  On December 1, two of its sensor sent back a “haunting low rumble” due to vibrations on the spacecraft’s solar panels from the 10-15 mile per hour (5-7 meters per second) winds blowing past the spacecraft. InSight Principal Investigator Brune Banerdt called it “an unplanned treat.” [https://www.nasa.gov/press-release/nasa-insight-lander-hears-martian-winds]

InSight has very sensitive instruments to detect Marsquakes (a seismometer) and meteorological data (an air pressure sensor).  The seismometer is still on the deck of the spacecraft.  It will be placed onto the surface using a robotic arm in the next few months.  While on the deck, its short-period silicon sensors can detect vibrations up to 50 hertz, at the lower range of human hearing.  The air pressure sensor detects vibrations at about 10 hertz, below the range of human hearing.  Scientists raised one set of signals by two octaves and sped up the other one to shift it up in frequency to make it audible to human ears. [https://www.nasa.gov/press-release/nasa-insight-lander-hears-martian-winds]

Voyager 2 Goes Interstellar

Voyager 2 long ago reached its intended destinations — Jupiter, Saturn, Uranus and Neptune.  Launched in 1977, Voyager 2 and its twin, Voyager 1, are still transmitting data back to Earth as they continue on their journeys to parts unknown.  Voyager 1 crossed into interstellar space in August 2012. Voyager 2 has now achieved the same milestone, although it is headed in a completely different direction.  It is slightly more than 11 billion miles (18 billion kilometers) from Earth.  A signal takes 16.5 hours to travel that far.

Both spacecraft are powered by radioisotope thermal generators (RTGs) whose power diminishes by four watts per year, so some of their instruments have been turned off over the years to manage power.  They can still detect the solar wind inside the Sun’s “bubble,” however, and when it stops, they are in interstellar space.  As explained by Voyager Project Scientist Ed Stone (see the video in the tweet), inside the bubble the Sun’s plasma and magnetic field are dominant.  Outside the bubble the material comes from stars “that exploded 5, 10, 15 million years ago.”

While they are in interstellar space, they have not left the solar system and will not for hundreds of years, however.

While the probes have left the heliosphere, Voyager 1 and Voyager 2 have not yet left the solar system, and won’t be leaving anytime soon. The boundary of the solar system is considered to be beyond the outer edge of the Oort Cloud, a collection of small objects that are still under the influence of the Sun’s gravity. The width of the Oort Cloud is not known precisely, but it is estimated to begin at about 1,000 astronomical units (AU) from the Sun and to extend to about 100,000 AU. One AU is the distance from the Sun to Earth. It will take about 300 years for Voyager 2 to reach the inner edge of the Oort Cloud and possibly 30,000 years to fly beyond it. — NASA

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